This invention generally relates to bonding apparatus for mounting semiconductor chips with many, low-pitch projecting electrodes (i.e., bumps) onto a wiring substrate at high density. More specifically, it pertains to a bonding apparatus for bonding such semiconductor chips onto an opaque wiring substrate formed of such materials as silicon or ceramic by means of what is known in the semiconductor industry as "facedown bonding".
In the art, there is a bonding method known as the MBB (micro bump bonding) method in which a semiconductor chip having on its undersurface many, low-pitch bumps is mounted onto a wiring substrate having on its top surface wires so that a batch wireless bonding can be accomplished by means of the facedown bonding.
FIG. 5 illustrates a bonding apparatus of the MBB method. This bonding apparatus includes a mounting stand 2, a depression jig 4, a pressurizer 5, and several optical fibers 6. Placed onto the mounting stand 2 is a wiring substrate 1 of such materials as silicon or ceramic, the wiring substrate 1 having wires on its top surface. The depression jig 4 is used to depress against the wiring substrate 1 a semiconductor chip 3 with bumps 3a on its undersurface, the semiconductor chip 3 being set in place on the wiring substrate 1 that is placed on the mounting stand 2. The pressurizer 5 is disposed above the depression jig 4 and is used to push down the depression jig 4. The optical fibers 6, disposed alongside the depression jig 4, send out respective light rays upon a photo-curing resin (i.e., the resin which hardens on application of light) supplied between the wiring substrate 1 and the semiconductor chip 3. The mounting stand 2 is mobile, which facilitates the alignment of the semiconductor chip 3 with the wiring substrate 1, in bonding these two elements together. The depression jig 4 has a holder 7 and a depression chip 8. The depression chip 8 is made of hard metal, ceramic, or the like materials, and is jointed to the undersurface of the holder 7. The top surface of the holder 7, indicated by the reference numeral 7a, is jointed to the pressurizer 5.
FIGS. 6(a)-(d) shows shows how such a bonding apparatus mounts the semiconductor chip 3 onto the wiring substrate 1.
As shown in FIG. 6a, the wiring substrate 1, with its top surface up, is placed onto the mounting stand 2. Then, the top surface of the wiring substrate 1 is coated with a photo-curing resin 9 having the property of insulation. The wire 1a is of such materials as Cr, Au, Al, Cu, or like materials. The bump 3a, on the other hand, is of such materials as Au, Al, Cu, or like materials. For the photo-curing resin 9, such materials as ultra violet ray-curing epoxy resin, silicon resin, acrylic resin, or the like materials may be employed.
As shown in FIG. 6b, the semiconductor chip 3 is set in place on the wiring substrate 1, with the bump 3a of the semiconductor chip 3 aligned with the wire 1a of the wiring substrate 1 as well as with the photo-curing resin 9 disposed between the semiconductor chip 3 and the wiring substrate 1.
As shown in FIG. 6c, the downward movement of the pressurizer 5 causes the depression jig 4 to press the semiconductor chip 3 downward, whereby the semiconductor chip 3 is pressed against the wiring substrate 1. The photo-curing resin 9 lying between the bump 3a and the wire 1a therefore extrudes from between the bump 3a and the wire 1a. As a result, the bump 3a is brought into electrical contact with the wire 1a.
Thereafter, the optical fibers 6 simultaneously send out respective ultra violet rays upon the photo-curing resin 9, with the semiconductor chip 3 pressed onto the wiring substrate 1, whereby the photo-curing resin 9 hardens on application of the ultra violet rays. In other words, while making reflection and scattering between the undersurface of the semiconductor chip 3 and the top surface of the wiring substrate 1, the ultra violet rays enter the photo-curing resin 9 to harden it.
The several optical fibers 6 are provided around the depression jig 4, the reason for which is that the photo-curing resist 9 around the semiconductor chip 3 cannot simultaneously be hardened by only one optical fiber. If the optical fiber 9 is to be disposed outside every side of the semiconductor chip 3, this requires four optical fibers. If the optical fiber 9 is to be disposed outside every side and corner of the semiconductor chip 3, this requires eight optical fibers.
As shown in FIG. 6d, the pressurizer 5 has moved away from over the semiconductor chip 3.
The semiconductor chip 3 is now firmly fixed to the wiring substrate 1, and the bump 3a of the semiconductor chip 3 is brought into electrical contact with the wire 1a of the wiring substrate 1 due to shrinkage force of the photo-curing resin 9.
As shown in FIG. 7a, if there is a great space (i.e., the width W1) between a semiconductor chip 3A being depressed with the depression jig 4 and its neighboring semiconductor chip 3B, the optical fiber 6 is able to send out ultra violet rays through such a great space upon the photo-curing resin 9. A tilt angle, .theta., formed between an ultra violet ray emitted from the optical fiber 6 and one side face of the semiconductor chip 3A, is determined based on the efficiency of the hardening of the photo-curing resin 9 (FIG. 7a).
As shown in FIG. 7b, if the semiconductor chip 3A and the neighboring semiconductor chip 3B are mounted in close proximity, that is, if there is a close space (the width W2) between these two semiconductor chips, some ultra violet rays, given off from the optical fiber 6, are interfered with due to the presence of the neighboring semiconductor chip 3B. This presents a problem in that the efficiency of the irradiation relative to the photo-curing resin 9 lying around the semiconductor chip 3A decreases.
As shown in FIG. 7c, a depression surface 8a (i.e., the undersurface of the depression chip 8) is generally given a slightly greater area compared to the semiconductor chip 3 so that even though the relative positions of the depression jig 4 and the semiconductor chip 3 deviate, the depression surface 8a of the depression chip 8 can manage to equally depress the semiconductor chip 3. This, however, presents another problem in that some ultra violet rays, given off from the optical fiber 6, are interfered with by the depression surface 8a the area of which is greater than that of the semiconductor chip 3. This results in the decrease of the efficiency of the irradiation relative to the photo-curing resin 9.